Cormier has repeatedly stated that he wanted to face a high-quality opponent. He expressed concern that Strikeforce's recently depleted heavyweight roster would make it difficult for the promotion to satisfy his demand.
"I got exactly what I asked for," Cormier told ESPN.com. "No matter who they put in front of me, I was going to prepare myself like a professional and get ready to fight. But I just did not know, with everything that has been said about guys crossing over (from Strikeforce to UFC), if they were going to be able to find someone who fit how my career has played out.
"My career has played out where I've advanced at every step, from one guy to the next to the next. I wasn't sure if there were too many guys outside of UFC who fit that. Frank Mir does that and even more.
"He's a guy I have a great amount of respect for, all of his accomplishments and what he's done lately. I get to fight the guy who just fought for the UFC championship two months ago."
USA Today first reported the news Wednesday night. UFC's parent company, Zuffa, purchased Strikeforce in March 2011 and UFC president Dana White pledged to operate the two companies independently, vowing not to send Strikeforce fighters to the UFC. As part of the deal, Strikeforce would remain on Showtime through 2012.
"There has been a lot of speculation as to who Cormier would fight next, and this is the fight that makes the most sense," White told the newspaper. "The reality is, Cormier is one of the best heavyweights in the world.
"He just won the grand prix and beat Josh Barnett. He needs to fight opponents of that caliber, and Frank Mir is that guy."
Cormier is 10-0 as a professional mixed martial artist. His bout with Mir will be the final heavyweight fight under the Strikeforce banner.
Mir is a two-time UFC heavyweight champion. He first claimed the title June 19, 2004, with a first-round armbar submission of Tim Sylvia.
In his most recent outing, Mir was on the wrong end of a second-round TKO to current UFC heavyweight titleholder Junior dos Santos. That fight was held May 26 at UFC 146.